The present disclosure relates to a stacker and a method to assemble a stator core of an electric machine. Disclosed is a method for stacking a stator core of an electric machine, with the steps of providing a support adjacent to the stator frame to carry at least a sheet for the stator core, grabbing the at least a sheet with an arm arranged outside the stator core, the arm has a holding device for clamping the at least a sheet, guiding the at least a sheet inside the stator frame in a horizontal direction, and arranging the at least a sheet to compose the stator core.